This is the first time I've asked for help online, but my B16 transplant engine is over-heating. I replaced all of the relays, sensors, and the thermostat and it still overheats in 5 min. of driving. Usually when I start to overheat, I can dissipate some of the heat by turning on the heater, but now the heater just blows luke warm air. Also, the upper rad hose gets very hot while the lower hose stays cool. Some ideas I have are: bad water pump, clogged radiator(but it's brand new), or maybe I somehow installed the thermostat wrong and the spring isn't activating. The old thermostat activated at 180 deg and the new one is set at 170 deg(which I thought was better, but?)HELP!?

 

I think you definitely have a coolant leak, probably just too small to see clearly. I had that same problem, and it turned out to be a coolant leak out of a very small hose w/ the smallest little slit ever. Everytime i revved up, coolant would spray out like crazy from this small little slit.

 

Actually I would take the radiator cap off (of course when the car is cool) and start the car. You may have some left over bubbles in the system causing the coolant not to circulate correctly. Since you just installed a new radiator.

 

There's an idea too, but you really need to pop the hood and rev it up and see if you can find any coolant gushing out from any lines. Im telling you, it doesnt take much too spray it everywhere.

Could also be a headgasket problem. Idk...

 

water pump?

 

In order of ease of checking:

1) bubbles in radiator - do what I say above. Takes about 10-15 minutes. Just add coolant - $9?
2) head gasket - can drain oil to see if you can see coolant in your oil
3) water pump
4) also could be plug like my 1993 Civic Ex had. Some how the plug from the car to the radiator fan was damaged. The car's temp skyrocketed unless I was driving (and I was in NYC in traffic).